The visit came after a bet in which Evans -- a diehard Patriots fan -- agreed to show up in costume if his team lost to the Seattle Seahawks in the Super Bowl. Pratt, for his part, promised to come to Christopher's Haven, a Boston-area pediatric cancer center, if his team -- the Seawhawks -- lost, dressed as Star Lord, his "Guardians of the Galaxy" character.

Over the weekend he fulfilled that promise, and the kids loved every minute of it, parents told the hospital.

"We were so surprised," said the mother of Tyler, a 14-year-old patient being treated for leukemia. "It gave Tyler five minutes of happiness. This situation will never be normal, but their visit helped make us feel special."

The bet helped raise more than $27,000 for Seattle Children's and Christopher's Haven, the Seattle Hospital said.